Our environment can affect our health with both short-term and long- term effects. In our society, a major concern is environmental contaminants in the air we breathe. Our laboratory focuses on the neurotoxic effects of 2, 3, 7, and 8-tetrachlorodibenzo-p-dioxin (TCDD) and benzo(a)pyrene [B(a)P]. TCDD is a polychlorinated dibenzo-P- dioxin, the most biologically potent member of the halogenated aromatic hydrocarbons (HAH). B(a)P is a member of the polycyclic aromatic hydrocarbon family. Both are formed as combustion by-products and have been reported to initiate carcinogenesis in animals and humans. TCDD and B(a)P are agonists of the aryl hydrocarbon receptor (AhR) and have been shown to induce cytochrome P450 1A1/1A2. Gestational exposure to these environmental contaminants independently has been shown to cause developmental and behavioral deficits. Therefore, we are studying the effects of transplacental exposures to TCDD/B(a)P mixtures. The objective of this study is to determine the effects of TCDD/B(a)P mixtures on learning and memory. We hypothesize that gestational exposure to TCDD/B(a)P mixtures causes deficits in learning and memory. We anticipate that mixed TCDD/B(a)P exposures will show deficits in cognition manifested as increased in patency in radial arm and maze assessments. LTP decrements and dysregulation of AhR, ARNT, and CYP 1A1/1A2 in the developing nervous system. These results will suggest that environmental mixtures play an antagonistic role in the development of the CNS.